Phase meter



June 5, 1956 J. R. RAGAzzlNl ErAL 2,749,516

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PHASE METER 7 Sheets-Sheet 4 Filed June l2, 1950 ATTORNE 5 7 Sheets-Sheet 5 J. R. RAGAZZINI ET AL PHASE METER RNE;

INVENTOR. Joh/7i?. RaqaZZ/n/'a//d Lofri A. Zai/eh Y M, @W4 ATTU June 5, 1956 Filed June l2, 1950 June 5, 1956 J. R. RAGAzzlNl Erm. 2,749,516

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ATTORNEY 7 Sheets-Sheet 7 J. R. RAGAZZINI TAL PHASE METER IN VEN TOR. John l?. Ragazzi/w' and Lo/ff A lade/7 BY W, @w+ @W7 A T TORNE )f5 June 5, 1956 Filed June 12, 1950 nited States Patent PHASE METER John R. Ragazzini and Lofti A. Zadeh, New York, N. Y.

Application June 12, 1950, Serial No. 167,550

Claims. (Cl. 324-88) This invention relates to a method of measuring the phase angle between two voltages and to apparatus for making such measurements.

An object of the invention is to provide an improved phase meter having a direct reading calibrated phase shifter.

Another object is to provide a phase meter having a phase angle scale which is independent of frequency.

A further object is to measure phase differences with high precision over a wide range of frequencies,

Another object is to provide a phase meter of relatively simple construction adapted for high precision phase angle measurements, and adapted for very simple construction at low cost when measurements of relatively low precision are adequate.

Another object is to measure phase angle differences over a broad band of frequencies without requiring the use of a heterodyne operation and the complications and diiculties inherent with such a heterodyne operation.

Another object is to provide a phase meter in which the actual measurement of phase is accomplished by a single control element, all other control operations being auxiliary to the adjustment of voltage and independent of the actual setting of the phase angle measurement control element.

These and other objects and features of the invention will be understood from the following detailed description in connection with the accompanying drawings, in which:

Fig. l is a schematic circuit diagram showing the general arrangement for making phase angle measurements;

Figure 2 is a circuit diagram of a phase shifting amplifier of the integrator type, andFig. 3 a similar'diagram of a phase shifting amplifier of the differentiator type.

Figures 4 and 6 are schematic diagrams of calibrated phase Shifters adapted for use inthe phase meter of Fig. l. l

Figures 5 and 7 are vector diagrams illustrating the operation of the circuits of Figures 4 and 6, respectively;

Figs. 8A, 8B and 8C are circuit diagrams of one form of phase meter; and

Figs. 9A and 8B are circuit diagrams of a modiiied form of phase meter.

In Fig. 1 we'have indicated a simple form of block diagram fundamental to our invention. In this diagram E1. and E2 are the voltages the phase difference of which is to be measured. The voltage E2 is transmitted direetly to the vertical plates of a standard oscillograph 53. E1 is transmitted through two components, the first being a calibrated phase shifter 20, and the second being a non-calibrated phase shifter 21, the output of which is fed to the horizontal platesof the .oscillograph The method of measurement consists of first placing switch 30 in its upward position, so that the voltage E1 is supplied to both channels. The calibrated phase shifter is originally set to zero because the voltages are from the same source E1 and therefore have a zero phase difierence. The non-calibrated phase shifter 21 is now adjusted until the trace on the oscillograph 53 is a collapsed 2 ellipse, indicating that ythe phase shift in both channels is identical.

The switch is then thrown to the lower position, so that now voltage E1 is in the first channel and E2 is in the second channel. The collapsed ellipse is restored by adjustment of the calibrated phase shifter 20 until it is collapsed once again, and the amount of phase shift that had to be inserted in the calibrated phase shifter is the phase difference between the two voltages E1 and E2.

Fig. 4 shows one form of calibrated phase shifter which employs as a component thereof a phase shifting feed back amplifier of the integrator type, shown in Fig. 2,y in which the amplifier has the variable resistor R in the upper input conductor and the capacitor C connecting the upper input conductor to the upper output conductor. The input voltage Ea produces the output voltage Eb which is displaced 90 in a leading direction from the input voltage Ea. The precision of this 90 displacement is determined by the gain of the ampliiier A and the quality of the capacitor C.

Instead of employing a phase shifting feed back amplilier of the integrator type, as shown in Fig. 2, as a component of the calibrated phase shifter, a phase shifting feed back amplifier of the diferentiator type, as shown in Fig. 3, may be substituted therefor. It will be seen that the integrator of Fig. 2 is similar to the ditferentiator of Fig. 3, except that the resistor R and the capacitor C are iuterchanged in position in the two ligures. In the integrator type of amplifier, the output voltage leads the input voltage by 90, whereas in the diierentiator type, the output voltage lags 90 behind the input voltage.

The amplifier 29, Fig. 4, corresponds with amplifier A, Fig. 2; the variable resistor 26, Fig. 4, corresponds with the resistor R, Fig. 2; and Ithe capacitor 27, Fig. 4, corresponds with the capacitor C, Fig. 2. At the output of the amplier 29, Fig. 4, is provided an adjustable potentiometer 22, the output voltage Eb being impressed across this potentiometer. A summing network, consisting of resistors 23, 24 and 25, is used to add the voltage Ea and a fraction A Eb, of the voltage Eb. The adder resistors 23 and 24 are made closely equal to each other, preferably within 1% or better when high accuracy is desired. The variable resistor 26 corresponds to resistor R, Fig. 2, and capacitor 27, Fig. 4, corresponds to the capacitor C of Fig. 2,` v

.In the initial'adjustmentV of the phase-shifter, Fig. 4, the input voltage Ea is impressed across the input ceupling resistor 28. The magnitude of the output voltage Eb is adjusted to be precisely equal to that of Ea, by adjusting the resistor 26. This is achieved when the product RCw equals l, where w is 21r times the frequency, For example, in the vector diagram of Fig. 5, Eb is shown equal in magnitude to Ea and as leading Ea by The fraction AEL) of Eb that is added to Ea. will determine the phase 0 of the resultant vector Ec. 0 is precisely known from the relation En The potentiometer 22 is calibrated to indicate directly the angle 0 for each adjustment of the angle between AE1) and E9. in the calibrated phase shifter, the angle 0 in each case being equal tothe arc whose tangent is tan 6= Fig. 6 shows the manner in which the circuit of the calibrated phase shifter is altered so that the phase shift range can bc extended from 45 to 90. Again, the integrator type of circuit is used as an example, and the calibrated potentiometer 22 is now connected across the input voltage rsf., instead of across the output voltage En as in Fig. 4, and a fraction AEs of En is now added through the same summing network 23, 24, 25 to the full value of En.

lt will be noted that the coupling resistor 2S which is equal in resistance to potentiometer 22, is interchanged in position with potentiometer 22 to avoid undesirable changes in the circuit when these resistances are interchanged. While resistor 28 is not essential to the basic operation of the circuit of Fig. 6, it is desirable from the standpoint of good circuit design.

The vector diagram, Fig. 7, shows the angle 9 as being in the sector extending from 45 to 90. lt will be observed from the diagram that the angle 9 is now equal to the angle whose tangent is AEa Figs. 8A, 8B, and SC show a schematic diagram of a complete phase meter according to Fig. 1 and including a calibrated phase shifter of the integrator type according to Figs. 2, 4 and 6.

ln Fig. 8A, the voltage input terminals 40 and 41 have the voltage E1 applied thereto, and the voltage input terminals i2 and 43 have the voltage E2 applied thereto. The voltages E1 and E2 are shown as being derived from a circuit Sti under test, having a supply voltage Ei connected to the input terminals 44 and 45 thereof, and a voltage E2 at the output thereof. The purpose of this particular test circuit arrangement is to measure the phase difference between the input voltage E1 and the output voltage E2.

The switch 51 corresponds with the switch .3() in Fig. 1, except that the lower pole of switch ,30 is replaced by a permanent connection between the lower terminals for E1 and E2.

The calibrated phase .shifter of Fig. l is included in the circuit of Fig. 8B. The non-calibrated phase shifter 21 of Fig. l is included in the circuit of Fig. 8C. The oscillograph 53 of Fig. l is shown also in Fig. 8C.

The lower channel conductors 54 and 55 in Fig. l, which connect drectly to the vertical deiiecting input terminals of the oscillograph 53, correspond to the conductors 54 and 55 in Figs. 8A, SB and 8C. The upper channel conductors 56, 56a and 5611 of Fig. l .correspond to conductors 56 and 56 in Fig. 8A, conductors 56 and 56a .in Fig. 8E, and conductors 56a and 56h in Fig. 8C, while conductors 57, 57a and 57!) in Fig. 1, correspond to conductor 55 in Figs. 8A, 8B and 8C.

In Fig. 8A the switches 60 and 61 have the four po sitions (a), (b), (c) and (d), respectively, and are ganged together to operate in unison as indicated by the dotted line 62. When the switch 60 is in position (a) or (b), the input potential applied to terminals ttl-41 Ei connects with channel 5S, 56. When in positions (c) `and (d), switch 60 connects the input potential applied to terminals t0-41 El with Vthe other channel 54, 55. Switch 61, when in positions (a) or (b), connects the other input potential Ez with channel 54, 55, and in positions (c) or (d) connects E2 with channel 5,5, 56.

When input Vpotential E1 connects with channel 55. 56 with switch 6i) in positionV (a) or (b), the voltage Ei is transmitted through the capacitor 63 to the potentiometer 64, whose sliding Contact 65 connects with the grid of triode 66, having the grid leak resistor 69. The cathode follower resistor 67 is `coupled by the ca` pacitor 63 with conductor 56 which extends to the calibrated phase shifter shown in Figure The triode 66 serves as an isolating stage to provide the desired impedance transformation between the source 4 Ei or Ez and the input conductors 55, 56 of the calibrated phase shifter circuit of Fig. 8B.

A suitable source of current, such as the alternating current rectifier 70, Fig. 8A, is provided for energizing the direct current circuits of the electron discharge deviccs of Figs. 8A, 8B and 3C, the cathodes being heated in well known manner by the usual heater element, not shown.

ln the calibrated phase shifter of Fig. 8B, the electron discharge devices 71, 72 and 73 serve as voltage amplihers, corresponding in function with the amplier 29 in Figs. 4 and 6. The fixed resistor 74 is connected to conductor 56 and in series with the fixed resistor 75 shunted by the variable resistor 76. Resistors 74, 75, 76 provide a variable resistance network connecting conductor 56' to the grid of triode 7l and to conductor 84, and corresponding with the variable series input resistor 26 in Figs. 4 and 6.

The capacitors 3G, Si, S2, S3, Fig. Si', of different capacitance values are selectively connectable one at a time in series with the conductor 34, by the rotary switch 8S, which has the four contact positions (a), (b), (c) and (d), respectively, the selected capacitor corresponding with feed-back capacitor 27, Figs. 4 and 6.

The triode 71 is provided with a cathode follower resistor 86, which is included in the cathode to control grid circuit of pentode 72, and thus serves as a coupling between the output of triode '71 and the input of pentode 72. Resistor 86 is shunted by the capacitor 87. The grid leak resistor 110, for the grid of triode 71, is connected between conductors 56 and 55. The anode of triode 71 is supplied with a positive potential by rectifier 70 (Fig. SA).

The positive screen grid potential in pentode 72 is reduced to the proper value by resistor fig, connected to rectifier 70, a bypass capacitor 89 connecting the screen grid with grounded conductor 55. The suppressor grid of pentode 72 is connected directly with the cathode. The anode of pentode 72 is connected through output resistor 9i) with a positive terminal of the rectifier 70 (Fig. 8A). The output of pentode 72 connects from the anode thereof to the left terminal of capacitor 91 which is shunted by a circuit comprising a resistor 92 in series with a capacitor 913, the right hand terminal of capacitor 91 being connected through resistor 94 with the control grid of pentode 73.

The cathode of pentode 73 has a voltage dropping resistor' 9S, shunted by the capacitor 96. The screen grid is connected through resistor with a positive terminal of rectifier 7@ (Fig. 8A), a bypass condenser' 98 being connected between the screen grid and ground ed conductor 55. The suppressor kgrid is connected directly with the cathode, while the anode is connected through the output coupling resistor 99 with a positive terminal of the rectifier 76, the anode being also connected to switch arrn 85. Resistor 94 connects from the control grid of pentode 73 through the leak resistor' 100 to the conductor 55.

Switches 101 and 162 have four positions (d), (b), (c) and (d), and are coupled together to operate in unison, as indicated by the dotted line 163. and are also coupled with switches 6i) and 61, Fig. 8A, as indicated by the dotted line 120.

When switch 101 is in the position (a) `or (d) it connects the anode or output circuit yof pentode 73 through contact (a) or (d) of switch MF1 with potentiometer 104, and from the slider through resistor 106 to the output conductor 56a, while switch `102 in position (d) or (d) connects the input conductor s6' through contact (a) or (d) of switch 192 through rcsistor 1.07 with the output conductor 56a of :the calibrated phase shifter. The connection from ,the output conductor 56a to the input conductor 56', provides a feed back from the output to the input of the phase shifter, `as indicated in Fig. .4, by the conductor includ ing resistor 24. Potentiometer 104, Fig. 8B, corresponds with potentiometer 22, Fig. 4. Resistor 108, Fig. 8B, provides an output coupling across the output conductors 56a and 55 of the calibrated phase shifter. The resistors 106, 107 and 108 are adder resistors corresponding respectively with the adder resistors 23, 24 and 25, Fig. 4. Resistor 109, Fig. 8B, corresponds with the dummy load resistor 28 in Fig. 4.

When switches 101 and 102 are in positions (b) or (c), the potentiometer 104 and resistor 106 are transferred from the output of the amplifier, as shown schematically by potentiometer 22 and resistor 23 in Fig. 4, to the input of the phase shifter, as shown schematically in Fig. 6, and the resistors 107 and 109 are transferred from the input of the phase shifter, as shown schematically by resistors 24 and 28, in Fig. 4, to the output of the amplifier as shown schematically in Fig. 6.

lfhe interstage coupling network 91, 92, 93, is adjusted to stabilize the operation of the amplifier by suppressing undesired oscillations.

In the non-calibrated phase shifter of Fig. 8C, the conductor 56a connects through the capacitor 150 with the grid of triode 151 which serves as an isolating stage to provide the desired impedance transformation between the calibrated phase shifter of Fig. 8B and the uncalibrated phase shifter of Fig. 8C. A resistor 152 connects the grid directly to the cathode of triode 151. The anode of triode 151 connects with a positive terminal of rectifier 70, Fig. 8A.

Coupling resistor 153 connects the grid of triode 151 to conductor 55. The cathode of triode 151 has a cathode follower resistor 154 which connects through a capacitor 155 to the coupling resistor 164 and also to the conductor 169.

Conductor 169 connects with the group 0f capacitors 156, 157, 158, 159 any one capacitor of which is selectable by the rotary switch 160, having respectively the four contact positions (a), (b), (c), (d).

The 180 phase shift switches 161 and 181 are coupled together as indicated by the dotted line 182, to operate in unison between contacts (a) and (b). 'Ihe grid of triode 162 connects through the leak resistor 163 to conductor 55, the grid also being connected to switch 161. The variable resistor 165 connects switch 160 to grounded conductor 55.

The cathode of triode 162 is provided with a cathode follower resistor 166 which is also included in the cathode to control the grid circuit of triode 167 and serves as a coupling between these triodes. The anode circuit of triode 162 is energized from a positive terminal of rectifier 70, Fig. 8A, and the anode circuit of triode 167 is energized through resistor 168 from a positive terminal of rectifier 70. The output circuit of triode 167 connects from the anode thereof through the capacitor 170 and the phase meter output resistor 173 to conductor 55, and also connects to the contact (b) of the rotary switch 171 which in turn connects with conductor 56h leading to the upper horizontal deecting input connection of oscillograph 53, the lower horizontal deiecting input connection of oscillograph 53 being connected to grounded conductor 55. The grid of triode 167 connects through the leak resistor 172 with grounded conductor 55, the grid also being connected to the rotary switch 131.

Conductor 169 connects through a variable resistor 175 to the rotary switch 176, having the four contact positions (a), (b), (c) and (d) connected respectively to the capacitors 177, 17S, 179 and 180, the other terminals of which are connected to conductor 55. Switch 176 is coupled with switch 160, Fig. 8C, to operate in unison therewith, as indicated by the dotted line 190, and in unison with switch 85, Fig. 8B, as indicated by dotted line 174.

The variable resistor 175, Fig. 8C, connects conductor 169m switch 176, and is coupled with variable resistor 6 165, as indicated by the dotted line 185', to permit of operation of these resistors in unison with each other.

It will be seen that resistor 165 in series with the capacitor selected by switch 160 from the group of capacitors 156 to 159, forms one arm of a bridge between conductor 169 and conductor 55. The other arm of the bridge includes the resistor 175 in series with switch 176 and the capacitor selected thereby in the group of capacitors 177 to 180. When switch 161 is in position (a) it will be noted that the grid of triode 162 connects with switch arm 160, While the grid of triode 167 connects with switch arm 176. When switch arm 161 is in position (b) the grid connections are interchanged, so that the grid of triode 162 connects with switch arm 176 and the grid of triode 167 connects with the switch arm 160.

Rotary switch 171 is provided with a contact (a) connected to conductor 137 connecting directly with the upper input conductor 56' of the calibrated phase shifter of Figure 8B, so that when switch 171 is in position (a), the input voltage of the calibrated phase shifter, which corresponds with voltage Ea in Figs. 4 and 5, is applied directly to the horizontal input of oscillograph 53.

When switch 171 is in position (c), the horizontal input of the oscillograph 53 is connected through contact (c) of switch 171 and conductor 188 with the anode of pentode 73, Figure 8B, so that the output voltage of the calibrated phase shifter amplifier, which corresponds with voltage Eb in Figs. 4 and 5, is applied directly to the horizontal input of the oscillograph 53. By comparing the oscillograph indications when switch 171 is in positions (a) and (c), the output voltage Eb of pentode 73 may be compared with the input voltage Ea across conductors 56', 55 and these voltages may be made equal by adjustment of resistor 76, Figure 8B, and by selection of the proper capacitors by the coupled switches of Fig. 8B, and 160 and 176 of Fig. 8C.

The non-calibrated phase shifting bridge arrangement, including the resistors 165 and 175, and the capacitors selected by switches and 176, combined with triodes 162 and 167, make it possible to shift the phase of the output voltage across coupling resistor 173 with respect to the input voltage across conductors 169 and 55 through any desired angle within a range of 180, it being merely necessary to shift the adjustment of the unitary controlled resistors and 175. The voltage across resistor 173 is equal to the diiierence between the voltage from the grid of triode 162 to the conductor 55 and the voltage from the grid of triodev 167 to the conductor 55, so that by throwing the unitary controlled switches 161, 181 from position (a) to position (b), the connections of the grids of these triodes areinterchanged and a phase shift of 189 is introduced in the output voltage across resistor 173 with respect tothat produced when switches 161 and 181 are in position (a).

Unitary controlled switches 85, Fig. 8B and 160 and 176, Fig. 8C, are frequency band switches for selecting capacitors of suitable value for use in different frequency bands, so that in any one position of these switches the capacitor selected by switch 85 has such a value that the product of 21r times the frequency, times the resistance of network 74, 75 and 76, times the capacitance of the capacitor selected by switch 85, equals l, or wRC=1, as previously described in connection with Fig. 4.

In'one example of a phase meter according to the circuit of Figs. 8A, 8B and 8C, the capacitors selected by the switch 35, covered the following frequency ranges:

Frequency range in C. P. S.

Capacitor From- 'I`o- The capacitors selected by switches 160 and 176 provide for the same ranges of frequency as those provided by the capacitors selected by switch 85.

Switches 60 and 61, Fig. 8A, together with switches 101 and 102, Fig. 8B, which all operate together under unitary control, make it possible to employ the potentiometer 104 of the calibrated phase shifter to measure phase angles extending over a 360 range. In order to extend the range of the calibrated phase shifter of Fig. 8B beyond the range from to -90, to cover the range from 0 to 490, it is merely necessary to interchange the connection of voltages Ei and E2. This method is free from the possibility of producing a false indication on the oscillograph 53, because if E2 leads Ei (that is, by 90 or less), the potentiometer 104 can be adjusted until the oscilloscope 53 displays a collapsed ellipse indication of the correct slope which is standardized to be the same slope for all measurements with the phase meter of Figs. 8A, 8B and 3C. lf on the other hand, Ez lags Ei (that is, by 90 or less), the phase shifter is not capable of ad justment to produce a collapsed ellipse of the correct slope on the oscillograph 53, and it is only possible to produce such an indication of a collapsed ellipse of the correct slope by interchanging E1, Ez. The switches 60, 61, Fig. 8A are provided for accomplishing this interchange of Ei and E2.

When the switches 60 and 61 are in position (a) the range covers from 0 to -45; in position (b), the range covers from -45 to -90; in position (c), the range is +45 to +90; and in the position (d), the range is zero degrees to -}45. The ranges so far described of these switches, thus extend from -90 through 0 to +90.

In order to extend the range of the phase meter to cover phase angles from -90 to \-1S0, and from +90 to -l-1S0, the unitary controlled switches 161 and 181, Fig. 8C, are switched from contacts (a) to (b), and 180 is then added to each reading of the angle on potentiometer 104, Fig. 8B.

When operating the phase meter of Figs. 8A, 8B and 8C, the following procedure may be observed:

The source of voltage E1 is first connected to the terminals 40 and 41 of Fig. 8A. Switch 60 and the other switches ganged thereto, are placed in position (a). Switch 171 is placed in position (a). The input voltage across conductors 55, 56 of the calibrated phase shifter of Fig. 8B is then made equal to the output voltage of the amplifier 73 by equalizing the indication produced on the oscillograph 53. The voltage equalization is accomplished by alternately connecting the switch 1.71, Fig. 8C, to positions (a) and (c) While adjusting the resistor "i6, Fig. 8B, and, it necessary, adjusting the positions of the switch 35 with its ganged switches. When the voltages are equalized, they correspond to the cqualized voltages En and Eb in Fig. 4, as previously described.

Switch 171 is then placed on (b), switch 161 at position (n), and switch 51 at its upper position. The potentiometer 104 is then sct on 0, that is, at its lower limit of adjustment.

The uncalibrated phase shifter of Fig. 8C is then adjusted by adjustment of the resistor 16S with its ganged resistor 175 until the oscillograph 53 displays a collapsed ellipse which slopes either upward or downward, this fact being noted for future reference as hereinafter explained.

The source of the voltage E, if not already connected, may then be connected to the terminals 42, 43, Fig. 8A. Switch 51 is then placed in its lower position. Potentiometer 104 is then adjusted through its 45 range, or until the oscillograph 53 displays a collapsed ellipse which slopes in the same direction as noted in the reference above. If the ellipse fails to so collapse, switch 60 is moved to position (b) and the potentiometer 104 is again adjusted in search of a balance, and if no such balance is obtained, as indicated by the oscillograph 53, switch 60 is moved successively to positions (c) and (d),

while repeating the adjustment of potentiometer E04. If no balance is obtained thus far, switch 161 is moved to position (b) and the above procedure of adjusting potentiometer 104 for each position of switch 60 is followed until a balance is indicated by the oscillograph 53. After observing a few measurements so that the operator becomes familiar with the operation of the phase meter, the procedure may be considerably simplified by turning switches 66 and 161 to their propel' final positions without going through all of the above described intermediate steps.

The potentiometer 1.04 is calibrated to read directly in angular measure, the phase shift introduced by thc calibrated phase shifter of Fig. 8B, the 0 to 45 calibration being read when switch 60 is in position (a) or (d) and a to 90 calibration being read when switch 60 is in position (b) or (c). A minus sign is placed before thc angle reati on potentiometer iti/l when the phase balance is obtained with switch in position (a) or (b), and a positive sign is placed before the angle, if the balance is obtained when switch 60 is in position (c) or (rt). if the balance is obtained with switch 161 in position (n) nothing is added to the reading of potentiometer 104, while if switch 161 is in position (b) when the balance is obtained, is added to the angle reading.

Further measurements of the phase angle between 'di and E2 may now be made by merely adjusting the potentiometer i014 as long as the angle being measured remains within ythe 45 range of the potentiometer, for any given position of switch 60. If the phase angle to be measured extends outside of the 45 range of potentiometer 104 for which the switch 60 is set, it is then merely necessary to operate the switch 60 to its proper position and to malle any needed operation of the switch 1M within the wide frequency range corresponding to any one setting of the hand switch S5.

it will be seen that after preliminary adjustment of the phase meter, the phase angle between the voltages E1 and E2 can be accurately measured by merely adjusting a single control element, namely potentiometer 104, and reading its scale. If, after the preliminary adjustment, the phase angle between E1 and E2 has changed but the frequency of E1 and E2 is the same, the only control that need be operated to make the measurement is the potentiometer 104. if the amplitude of either El and/or E2 change but the frequency and phase angles of E1 and E2 remain the same, no change in the adjustment of the control element 104 need be made. lf the frequency changes after the preliminary adjustment, the meter must be completely readjusted. However, the dial calibration of the potentiometer 04 remains the same at all frequencies within the operating frequency range of the instrument.

Figs. 9A and 9B illustrate a circuit similar to that of Figs. 8A, SB and 8C, except that the differentiator type of calibrated phase shifter is employed, as shown schematically in Fig. 3, in place of the integrator type, shown in Fig. 2. it will be noted that some of the parts in Figs. 9A and 9B which are similar to corresponding parts in Figs. 8A, 8B and 8C, are given the same reference numerals distinguished by primes. vit will be also noted that in Figs. 9A and 9B, the input voltage Ei and thc input voltage Es are interchanged from the positions shown in Fig. 8A, so that when the ganged rotary switches 2.00 and Zhi, in Fig. 9A, are in the position (a), the voltage El is connected directly from ir. terminals 262 and 293 to the vertical detlecting inpu terminals of the oscillograph 53, Fig. 9B, over a path which may be traced from the upper input terminal 20?, for voltage E1, the lower contact of switch 204, to switch 2&4 and conductor 205 to switch 20?., through Contact (a) of switch 201 and conductor 206, to the upper vertical deilecting terminal of oscillograph 53, and returning from the lower vertical deecting terminal of oscillograph 553, to grounded conductor 208, leading to conductor 207 and terminal 203,

Fig. 9A. The described path for voltage E1 thus corresponds with the lower channel in Fig. 1.

The voltage E2 in Fig. 9A is connected at input terminals 210 and 211, through a calibrated phase shifter, Fig. 9A, and a non-calibrated phase shifter, Fig. 9B, to the horizontal defiecting input terminals of the oscillograph 53, Fig. 9B, similarly to the connection in Fig. 1 of voltage E1 to the horizontal deecting input terminals of the oscillograph 53. The path for voltage Ez in Figs. 9A and 9B may be traced from the upper input terminal 10, to switch 200, over contact (a), conductor 212, isolating amplifier 213, conductor 214, voltage amplifiers 215, 216 and 217 in cascade in the calibrated phase shifter, over output conductor 218 of the calibrated phase shifter, and then to Fig. 9B, over isolating amplifier 151', to conductor 220, forming the input conductor of the non-calibrated phase shifter, including electron discharge devices 162' and 167' to the output conductor 223, connected to the upper horizontal defiecting input terminal of oscillograph 53. The return path from the oscillograph may be traced from the lower horizontal terminal thereof, over conductor 208, to Fig. 9A, and directly to the lower input terminal 211 for the voltage E2.

In Fig. 9A, the isolating amplifier 213 corresponds in function with the isolating amplifier 66 in Fig. 8A, and includes similar elements in its circuit connections, as indicated by the same reference numerals with primes. The voltage amplifiers 215, 216, 217 in the calibrated phase shifter in Fig. 9A, correspond with amplifiers 71, 72, 73 in Fig. 8B, and employ circuit connections which are similar to the amplifiers 71, 72, 73, Fig. 8B, except as will be noted hereinafter. The isolating amplifier 151', Fig. 9B, corresponds with the isolating amplifier 151 in Fig. 8C. The non-calibrated phase shifter triodes 162' and 167' in Fig. 9B, correspond with triodes 162 and 167 in Fig. 8C. Conductors 223 and 208, Fig. 9B, connected to the horizontal deflecting input terminals of oscillograph 53, Fig. 9B, correspond with conductors 56h and 55, respectively, in Fig. 8C.

Rotary switches 230 and 231, Fig. 9A, are coupled together to operate in unison, as indicated by the dotted line 232, and are also coupled with switches 200 and 201, to operate in unison therewith as indicated by the dotted line 233. Switches 230 and 231, Fig. 9A, correspond with swi-tches 101 and 102, Fig. 8B. Conductor 214 is connected to capacitors 235, 236, 237 and 238, any one of which is selectable by the rotary switch arm 239, having the contacts (a), (b), (c) and (d). Switch 239 connects through the coupling capacitor 240 with the grid of triode 215, having the grid leak resistor 219.

The cathode follower resistor 241, connected between the cathode of triode 215 and conductor 208, is included in the cathode to control grid circuit of pentode 216 to provide a coupling between triode 215 and pentode 216. The pentode 216 has an output coupling resistor 224 in its anode circuit. The anode of pentode 216 connects through the capacitor 242 to the control grid of pentode 217. The resistor 243 in series with the capacitor 244 is connected in shunt with the capacitor 242 to provide a stabilizing network, corresponding with the network 91, 92, 93 in Fig. 8B.

The pentode 217, Fig. 9A, corresponds generally with the pentode 73, Fig. 8B, but it will be noted that the resistor corresponding with resistor 94, Fig. 8B, is omitted from Fig. 9A, and that the capacitor 245, Fig. 9A, which is included between the control grid and the anode of pentode 217, has no corresponding element in Fig. 8B.

Switch 239 connects through resistor 250 in series with resistor 251 to the anode of pentode 217, Fig. 9A, the resistor 251 being shunted by the variable resistor 252. The resistor network 250, 251, 252, corresponds with the variable resistor R in Fig. 3. The capacitor selected by switch 239, corresponds with the capacitor C in Fig. 3. The anode and other direct current circuits of triodes 213 and 215, and of pentodes 216 and 217 are energized from a suitable D. C. source, such as the rectifier 255N con' nected to an alternating current source.

The rectifier 255 has the transformer 400 with the primary 401 connected to the alternating current source, the secondary 402 having the grounded mid-tap 403, and the cathode heating secondaries 404 and 405. The terminals of secondary 402 are connected respectively to the two anodes of the rectifier tube 406, the cathode of which is heated from secondary 404 and is connected through the inductance 407 and capacitor 408 to ground. Elements 407 and 408 comprise the first section of a ripple suppressing filter having in cascade therewith a second section comprising inductance 409 in series with capacitor 410, and a third section comprising the resistor 411 in series with the capacitor 412 having the resistor 413 in shunt therewith. The screen grid of pentode 216 is connected through resistor 414 with terminal 415 of the rectifier filter, the capacitor 416 being connected between the screen grid and grounded conductor 208, the screen grid of pentode 217 being connected through the resistor 417 with the terminal 415, the capacitor 418 being connected between the screen grid and conductor 208.

The pentode 217 has a leak resistor 256 connecting its control grid with conductor 208, and has a cathode dropping resistor 257 shunted by the capacitor 258. The output coupling resistor 253 is connected between the anode of pentode 217 and rectifier 255. The anode of pentode 217 is connected to switch 230 which, in position (a), connects through potentiometer 259 with conductor 208. The sliding contact 260 on potentiometer 259 connects through resistor 261 to conductor 218. The output coupling resistor 262 of the calibrated phase shifter of Fig. 9A, connects conductor 218 with conductor 208. Conductor 214, at the input of the calibrated phase shifter, connects with conductor 263 leading to switch 231 which, in position (a), connects with conductor 264 which in turn connects through resistor 265 tov conductor 218. Conductor 264 also connects through resistor 266 to conductor 208.

The measuring potentiometer `259 corresponds with measuring potentiometer 104, Fig. 4. The combination of resistor 261, resistor 265 and resistor 262, Fig. 9A, provide an adder network, corresponding with the adder network in Fig. 4, including respectively, resistors 23, 24, 25. Resistor 266 serves as a dummy load for compensating for the transfer of potentiometer 259 from the output to the input of the calibrated phase shifter by means of switches 230 and 231, and corresponds with resistor 109, Fig. 8B.

The non-calibrated phase shifter shown in Fig. 9B is similar to that of Fig. 8C, except that switches 161 and 181 of Fig. 8C are omitted and permanent connections are provided corresponding with the circuit when switches 161 and 181 are in position (a). It will be noted that the frequency band switches 176', Fig. 9B are coupled together as indicated by dotted line 190, and are also coupled as indicated by dotted line 174 with switch 239, Fig. 9A, so that switches 239 (Fig. 9A) an 160', 176' (Fig. 9B), correspond respectively with switches 85 (Fig. 8B) and 160, 176 (Fig. 8C). Y

Instead of employing oscillograph 53 for indicating equality of the input and output voltages of the calibrated phase shifter in Fig. 9A, in the manner indicated in Figs. 8B and 8C, wherein switch 171, in its positions (a) and (c), connects the oscillograph with the input and output, respectively, of the phase shifter, a switch 270, Fig. 9A, in its upper position (a), connects the conductor 214, at the input of the calibrated phase shifter, with one terminal of a suitable voltage indicating device, such as the vacuum tube voltmeter 271, the other terminal ofthe voltmeter 271 being connected to conductor 272, leading to conductor 208. Switch 270 in its lower position (b), connects the voltmeter 271 to the output of the amplifier of the calibrated phase shifter. at the anode of pentode 217. The input and output voltages of the amplifier may be adjusted to equality by operating switch 270 alternately to positions (a) and (b) while adjusting the variable resistor 252 and frequency band switch 239, Fig. 9A, until the voltmeter 271 indicates the same voltage for both positions of switch 270.

When operating the phase meter of Figs. 9A and 9B the procedure is similar to that already described in connection with Figs. 8A, 8B and 8C. The source of voltage Ei, however, is temporarily connected with terminals 21% and 211. Switch 26@ and the other switches ganged thereto are placed in position (a). The input voltage lis in the calibrated phase shifter (see Fig. 3 for general schematic diagram) between conductors 214 and 205, Fig. 9A, is then adjusted to equality with the output voltage Eb of the amplifiers 215, 216, 217 of the calibrated phase shifter between the anode of pentode 217 and conductor 20S. Equalization of E@ and En is obtained by alternately positioning switch 27@ in position (a) and (o), while adjusting resistor 252 and switch 2312, as referred to above.

Switch 2M is then placed in its upper position. Potentiometer 259 is set on that is, at its lower limit of adjustment.

The uncalibrated phase shifter of Fig. 9B is then adjusted by adjustment of the resistor 165' with its ganged resistor 175' until the oscillograph 53 displays a collapsed ellipse in the form of a line which slopes either upward or downward, this fact being noted for future reference, as further explained hereinafter.

The source ot voltage E1 is now removed from terminals 21@ and 211 and the source of voltage E2 is connected in place thereof, the source E1 being connected with the terminals 202 and 203, as indicated in Fig. 9A. Switch 294- is then placed in its lower position. Potentiometer 259 is adjusted through its 45 range, or until the oscillograph 53 displaces a collapsed ellipse. lf the ellipse fails to collapse, switch 200 is then operated to its next position and the potentiometer adjustments repeated, and so on for each position of switch 2110 until a phase balance is indicated by a collapsed ellipse on the oscillograph.

The setting of potentiometer 259 is then read from its 0 to 45 calibration, if switch 20@ is in position (a) or (d), and is read from its 45 to 90 calibration, it switch 200 is in position (b) or (c). A positive sign is placed before the angle reading of potentiometer 25? when the switch 280 is in position (a) or (b), and a negative sign is placed before the angle reading if the balance is obtained when switch 20d is in position (c) or (d).

lf the collapsed ellipse on oscillograph 53 slopes upward white originally the slope of the collapsed ellipse referred to above was downward, or vice versa, 180 is added to the reading of potentiometer 259. By observing the direction of the slope of the collapsed ellipse on the oscillograph 53, it will be seen that it is unnecessary to introduce a reversal of phase in the non-calibrated phase shifter, is accomplished by switch 161 in Fig. 8C. The non-calibrated phase shifter is thus more siniplilied in Fig. 9B than in Fig. 8C. It will be understood that the switches 161 and 131, Fig. 8C, may be lett in position (a), or the circuit permanentiy connected in this form, without providing these switches, the neessity of adding 180 to the reading of the phase angle being determined as in the case of Figs. 9A and 9B.

While the present phase meter is capable of operating over the extremely broad frequency bands heretofore described, the term substantial range of frequencies" as used in the claims is not to be construed as limited to such broad frequency bands, but is intended to designate frequency ranges differing substantially from the useable frequency ranges of phase meters which are designed for operation at only a single frequency. Hence the term "substantial range of frequencies may be understood to mean a frequency range of at least 1.1 to l.

l2 The following are the values of resistors, capacitors, and other elements and voltages illustrative of one example of a phase meter constructed in accordance with the circuit of Figs. 9A and 9B. It will be understood, however, that various other values of the circuit elements can be used in other examples of this circuit.

Resistors Reference numerals: Value in ohms 64'; 243; 251; 256 meg 1 153'; 163'; 219 500K 252 (variable) 500K 414; 417 250K 173'; 261; 265 200K 69'; 152'; 168' 100K 165';1"/"5 (variable) 100K 67'; 266 50K 259 (potentiometer) 50K 413 30K 224; 25s 25K 262; 411 20K 116'; 264; 250 10K 154 5K Capacitors Reference numerals: Capacitances at 100 412 at 30 216; 217; 408; 410; 416; 418 i/.fu 16 68'; 155'; 156'; 170'; 177'; 244 at 1 63'; 157'; 178'; 242 at .1 156'; 235; 240 at .O5 158'; 179' at .01 236 at .005 159'; 189' at .001 237 Mrf 500 233 /L/Lf-.. 100 245 /mf-.. 5

Inductors 4167; 409 henries-- l5 Tubes Reference numerals: Type 4116 5U4G 217 6AC7 213; 215 615 216 6SJ7 V oltages 461 (60 C. P. S.) 125 462 2X440 We have described what we believe to be the best embodiments of our invention. We do not wish, however, to be confined to the embodiments shown, but what we desire to cover by Letters Patent is set forth in the appended claims.

We claim:

l. A phase meter comprising means to indicate a predetermined phase ditference between two waves of voltage, a separate path to said indicating means for each of said waves; a calibrated phase shifter having the same calibration for a plurality of substantially different frequencies, said phase shifter comprising means in one of said paths for deriving from the voltage applied thereto two voltages accurately out of phase with each other at any of said frequencies, calibrated adjusting means for selecting any desired fraction of one of said two voltages from zero to a maximum value of said fraction and means for adding said selected fraction of said one voltage to the other of said two voltages and for transmitting the resultant of said added voltages to said indicating means over the path which includes said voltage deriving means; and adjustable phase shifting means in one of said paths for adjusting the difference between the phase shifts of said two paths to said predetermined phase difference when said calibrated phase shifter has a predetermined initial reading, whereby said calibrated phase shifter is enabled to maintain its calibration over said frequency range, said calibrated phase shifter being adjustable to produce said predetermined phase difference at said indicating means when said two waves of voltages are applied to said two paths7 respectively.

2. A phase meter according to claim 1, further comprising means included in one of said paths for shifting the phase of the voltage wave therein through an angle of 180 degrees.

3. A phase meter according to claim 1, further comprising manually operable means for changing the frequency operating range of said adjustable phase shifting means and of said voltage deriving means in predetermined relation to each other.

4. A phase meter according to claim 1, wherein said voltage deriving means includes a 90 degree phase shifter comprising an amplifier having an input and an output, a iirst impedance element connected in series with said input, and a feed-back path including a second impedance element connected directly from said output to said input.

5. A phase meter according to claim 4 in which said amplifier is of the integrator type, said rst impedance element being a resistor and said second impedance element being a capacitor.

6. A phase meter according to claim 4 in which said amplifier is of the diierentiator type, said first impedance element being a capacitor and said second impedance element being a resistor.

7. A phase meter for measuring the difference in phase angle between two potentials, comprising: a iirst substantially continuously adjustable means producing a phase shift of which the magnitude may be varied; a second substantially continuously adjustable means producing a further phase shift of which the magnitude may be varied, said first and said second adjustable means being connected in cascade relationship; measuring means including a calibrated scale operatively associated with one of said adjustable means for indicating the magnitude of the phase shift produced thereby; said one adjustable means having the same calibrationat substantially different frequencies indicating means for indicating a predetermined phase relationship between said two potentials; and circuit means for connecting one of said potentials to said indicating means simultaneously both directly and through said two adjustable means, said circuit means including switching means for selectively` changing said connections to connect one of said two potentials directly to said indicating means and simultaneously connect the other of said potentials to said indicating means through said two adjustable means.

8. A phase meter according to claim 7 in which one of said adjustable means comprises means for deriving from the potential applied thereto, two equal voltages differing accurately in phase from each other by an angle of throughout a substantial range of frequencies, selecting means for selecting any desired fraction of one of said two equal voltages from zero to the full voltage thereof, and means for adding said selected fraction of said one voltage to the other of said two equal voltages, adjustment of said adjustable means being effected by varying the value of said selected fraction of said one voltage, said calibrated scale being operatively associated with said selecting means.

9. A phase meter according to claim 8, further comprising manually operable switching means for selectively switching said selecting means to select said desired fraction from either of said two equal voltages.

10. A phase meter according to claim 8, further cornprising switching means operatively associated with said voltage deriving means for changing the effective range of said substantial range of frequencies to at least one other substantial range of frequencies.

References Cited in the file of this patent UNITED STATES PATENTS Armstrong July 6, 1937 2,086,421 .Tones et al July 6, 1937 2,176,120 Brown et al. Oct. 17, 1939 2,178,012 White Oct. 31, 1939 2,341,232 Norton Feb. 8, 1944 2,429,844 Rothman et al Oct. 28, 1947 2,436,479 Luck Feb. 24, 1948 2,451,796 Berkoff Oct. 19, 1948 2,477,023 Weaver July 26, 1949 2,525,448 Clarke Oct. 10, 1950 2,527,096 Howes Oct. 24, 1950 2,530,528 Kreer Nov. 21, 1950 2,576,818 Waynick Nov. 27, 1951 2,579,586 Kroft Dec. 25, 1951 2,622,127 Alsberg Dec. 16, 1952 FOREIGN PATENTS 631,203 Great Britain Oct. 28, 1949 OTHER REFERENCES Publication I: A Simple Variable Frequency Phase Measuring Device by J. C. West and I. Patts; Electronic Engineering, vol. 24, No. 295, September 1952, pages 402 and 403. 

